Conventionally, a demodulation device of magnetic data in which magnetic data recorded on a magnetic information recording medium are read and demodulation data are created has been proposed by the present applicant (see, for example, Japanese Patent Laid-Open No. 2013-25852). The demodulation device described in the Patent Literature includes a magnetic head which reads magnetic data recorded on a magnetic information recording medium and a data demodulation section in which magnetic data read by the magnetic head are demodulated and demodulation data are created. The data demodulation section includes a preliminary data creating section, which creates a plurality of preliminary data strings for creating demodulation data based on intervals, i.e., time intervals between peaks of an analog-shaped read signal of magnetic data outputted from the magnetic head, and a demodulation data creating section which creates demodulation data based on a plurality of preliminary data strings created in the preliminary data creating section. The preliminary data string is configured of first individual data of 5 bits specified on the basis of the intervals. The preliminary data creating section includes a data storage section in which an interval is stored each time a peak of a read signal is detected. Further, the preliminary data creating section stores a template in which a part of a plurality of bit patterns configured of second individual data of 5 bits is listed.
In the demodulation device described in the above-mentioned Patent Literature, an interval which is newly stored in the data storage section when a peak of a read signal is detected is set as a fifth interval to be determined (determined interval “5”), the fifth interval to be determined (determined interval “5”) having been stored in the data storage section when the peak of the read signal is detected is shifted to a fourth interval to be determined (determined interval “4”), the fourth interval to be determined (determined interval “4”) is shifted to a third interval to be determined (determined interval “3”), the third interval to be determined (determined interval “3”) is shifted to a second interval to be determined (determined interval “2”), the second interval to be determined (determined interval “2”) is shifted to a first interval to be determined (determined interval “1”), the first interval to be determined (determined interval “1”) is shifted to a fourth interval for calculation (calculation interval “4”), the fourth interval for calculation (calculation interval “4”) is shifted to a third interval for calculation (calculation interval “3”), the third interval for calculation (calculation interval “3”) is shifted to a second interval for calculation (calculation interval “2”), and the second interval for calculation (calculation interval “2”) is shifted to a first interval for calculation (calculation interval “1”).
Further, in the demodulation device, the preliminary data creating section executes an reference interval specifying step in which a first reference interval and a second reference interval are specified on the basis of an interval for calculation each time an interval is stored in the data storage section, a reference interval assigning step in which, for every second individual data, when a second individual data is “zero”, the first reference interval is assigned to a template and, when the second individual data is “1”, the second reference interval is assigned, a comparing step in which, five intervals to be determined and the first reference interval or the second reference interval assigned to the template are compared for every bit pattern and for every bit of the bit pattern, and a preliminary data specifying step in which a bit pattern corresponding to a preliminary data string is specified on the basis of a comparison result in the comparing step and the specified bit pattern is set to be the preliminary data string. Further, the demodulation data creating section specifies a first individual data of a first bit of the preliminary data string specified in the preliminary data creating section as a data for creating demodulation data and demodulation data are created on the basis of the data. The data specified in the demodulation data creating section is a data corresponding to a first interval to be determined.
As described above, in the demodulation device described in the above-mentioned Patent Literature, each time a peak of a read signal of magnetic data is detected, an interval is stored in the data storage section and demodulation of magnetic data is started. Further, in the demodulation device, a preliminary data string is specified by comparing five determined intervals stored in the data storage section with a first reference interval or a second reference interval assigned to the template, and a first individual data of a first bit of the specified preliminary data string is specified as a data for creating demodulation data. In other words, a plurality of determined intervals is used and thus, in the demodulation device, even when variation of a moving speed of a magnetic information recording medium is large or, even when recording density of magnetic data recorded on a magnetic information recording medium is low, magnetic data can be demodulated appropriately.
Magnetic data recorded on a magnetic information recording medium is, as shown in FIG. 11, commonly configured of a preamble, an effective data part where effective data are recorded, and a postamble. In the preamble and the postamble, magnetic data of all “0” are recorded. Normally, magnetic data of about 22 bits are recorded in a preamble and magnetic data of about 13-30 bits are recorded in a postamble.
In recent years, a magnetic information recording medium is used in various countries and regions and, in some countries and regions, a magnetic information recording medium may be used on which no preamble and no postamble are recorded, or a magnetic information recording medium may be used in which magnetic data recorded in the preamble and the postamble are 3 bits or less. On the other hand, since the demodulation device described in the above-mentioned Patent Literature is structured as described above, in a case that magnetic data are read from a preamble side, unless magnetic data of 4 bits or more are recorded in the postamble, magnetic data recorded in an effective data part cannot be demodulated to the last part. Further, in the demodulation device described in the Patent Literature, in a case that magnetic data are read from a postamble side, unless magnetic data of 4 bits or more are recorded in the preamble, magnetic data recorded in the effective data part cannot be demodulated to the last part. For example, in a case that magnetic data are read from a preamble side and a postamble is not recorded, in the demodulation device described in the Patent Literature, when the last peak of a read signal of magnetic data recorded in the effective data part is detected, no peak is detected afterward and thus demodulation of magnetic data is not executed and magnetic data of the last 4 bits of magnetic data recorded in the effective data part cannot be demodulated.